Carrier wave telephony system



Filed Dec. 17, 1958 ,DE/VOD.

s/GMXL Pacs/wp Patented Feb. 18, 1941 UNITED STATES PATENT OFFICE ommenWAVE 'rELErnoNY SYSTEM ford, Conn., as trustee Application December 17,1938, Serial No. 246,456

InGei-many December 27, 1937 4 Claims.

My invention relates to carrier-wave telephony systems.

More particularly, my invention is concerned with systems of the type inwhich the transmit 5 ters and/or receivers of the individual channelsare connected through iilters to a common transmission line, and inwhich signals are transmitted by transmission of a carrier-wave. whichis suppressed lduring the transmissionjgof conversation, or of a signalcurrent compriselwithin the conversation side-band.

The term signal currents is t0 be understood to include broadly anysignal currents which are produced in the transmitter and used tocontrol any signal circuit on the receiver side. Thus, this term alsoincludes the selective impulses used in automatic systems,

In systems of the above type it is the usual practice to feed the signalcurrents in the transmitter to the transmission conductor before feedingthem to the filter associated with the corresponding channel, while inthe receiver the signal circuit for each channel is connected behind thelter associated with this channel. Thus, the signal currents passedthrough both the lters on the transmitter side and the lters on thereceiver side. However, to avoid4 overlapping conversations the filtersare always so proportioned that for transmitting communications theytransmit substantially only the conversation side-band used in thechannel concerned. The attenuation at the carrier frequency is thenappreciable and asia result the signal currents are always weakened to aconsiderable extent by their passage through the filters. Moreover thisattenuation may vary considerable with temperature changes. With regardto these variations of attenuation the signal receiver must beconstructed to operate at different strength of the received signalcurrents and this involves diiiiculties. To avoid defective control ofthe signal circuit it is necessary to provide signal currents of largeamplitude, and be cause of the reduction of the amplitudes in theiilters, it has been necessary to produce in the transmitter signalcurrents of extremely high amplitudes, which increased the cost of thetransmitter. V

'I'he object of my invention is to overcome the above difiiculty and toallow a decrease in the amplitudes of the signal currents produced inthe transmitter, while at the same time obtaining a low attenuation ofthe signal currents and a reliable operation of the signal circuit.

In accordance with the invention, I pass the signal currents directly tothe transmission line,

or pass them through only a portion of the lters, and as a result avoidany substantial weakening of these currents.

In one embodiment of the invention I employ lters comprising twosections, of which the section connected to the transmission lineslightly attenuates the signal current frequency, and the other sectionproduces a high attenuation of this frequency. Furthermore, I preferablyso design the filter sections that they have high input impedances atthe connecting point of the signal receiver, and thus make itunnecessary to use matching transformers for connecting the signalreceiver.

In order that the invention may be clearly understood and readilycarried into eiect, I shall describe the same in more detail withreferencer to the accompanying drawing, in which;

Figure l is a schematic diagram of a portion of a carrier-wave systemembodying the invention, and

Fig. 2 is a schematic diagram of the filters of Figure 1.

In Figure l the speech currents are fed through conductors I and 2 to abridge modulator 3, and modulate a carrier-wave produced by anoscillator il, the carrier-wave at the same time being suppressed. Theoutput voltage of modulator 3 passes through a band-pass filter 5 to atrans mission line 8 connected to collecting buses 9 and I0 to which thetransmitters of other channels (not shown) are connected.

The lter 5, which comprises two sections 6 and 'I connected throughconductors II and I2, passes only one of the two side-bands of themodulated wave produced in modulator 3. Section 6 may be so designedthat it highly attenuates the 'carrier frequency together with thespeech frequencies lying below and slightly above the carrierfrequencysection `I may be so designed to offer a low and constant attenuation tothe signal currents, which in the present case are of carrier frequency.

The signal currents are supplied to conductors I I and I2, and for thispurpose there is provided a relay I3 controlled by a circuit comprisinga switch I4 and battery I5, and having two single-throw normally-openarms I 6 and Il. Arm I6 has its heel connected to one terminal ofoscillator i and is adapted to engage a fixed contact I9 connectedthrough a resistance I8 to conductor I2, and arm II has its heelconnected to the other terminal of oscillator 4 and is adapted to engagea xed contact 20 directly connected to conductor il. Thus, closure ofswitch I4 causes the carrier-wave produced by oscillator 4 to be appliedto conductors and l2 and hence through filter section 1 to line 3.

It will be noted that the signal currents do not pass through filtersection 6, which, as stated,

brings out considerable attenuation of the carrierwave. Filter section1, causes only a slight attenuation of the carrier-wave with the resultthat the signal ycurrent is not weakened to any appreciable degree byits passage through filter 5.

Instead of being connected to conductors and I2, i. e., between twosections of the filter, the contacts I9 and 20 can be connected to buses9 and |0 respectively.

'I'he transmission line 8 is connected to the buses 2| and 22 to whichreceiver systems for several other channels (not shown) may beconnected. As shown, the receiver system comprises a bandpass lter 23connected to buses 2| and 22 and comprising two sections 24 an'd 25connected through conductors 26 and 21 and corresponding to sections 1and 6 respectively of the transmitter system. The output of section 25is fed to a demodulator 28 whose output, after being rectified, ispassed through conductors 29 to the subscriber line.

Connected to conductors 26 and 21 is a signal receiver, which, however,could be connected directly to buses 2| and22. The signal currents inconductors 26 and 21 are supplied through a matching transformer 30 tothe grid circuit of a triode 3| whose plate circuit includes a band-passfilter 32 which is tuned sharply to the carrierwave. The output voltageof lter 32 is rectified by a detector 33 whose output controls theactuating circuit of a relay 34 having a single-pole normally-open arm35 which controls a signal circuit including a battery 36 anda bell 31.

A suitable construction of the lter 23 of Figure 1 is shown in Figure 2in which the lter section 25 comprises two inductances 38 and 40 and acondenser 39 connected in series with conductor 26, and an inductance 4|and a condenser 42 connected in series between conductor 21 and a pointbetween condenser 39 and inductance 40. The illter section 24 comprisesa condenser 43 and an inductance 44 connected in series with conductor26 and a condenser 45 connected between conductor 21 and a point betweencondenser 43 and inductance 44. The two sections are preferably sodesigned that there is a high impedance between sections. Because ofthis the matching transformer 30 of Figure 1 can be replaced by thesimple coupling resistance 46 of Figure 2.

'Ihe filter 5 of Figure 1 is constructed similarly to that of Figure 2with sections 6 and 1 thereof corresponding to sections 25 and 24respectively of Figure 2.

While I have described my invention with reference to specificapplications and examples, I do not wish to be limited thereto, butdesire the appended claims to be construed as broadly as is permissiblein view of the prior art.

What I claim is:

1. In a carrier-wave system for transmitting intelligence from amodulator located at a transmitter station to a demodulator located at areceiver station by means of suppressed carrier modulated waves, atransmission line interconnecting said transmitter station and receiverstation, a band-pass filter connected between said modulator and saidtransmitting line, a band-pass filter connected between said demodulatorand said transmission line, both of said lters transmitting only one ofthe two side bands generated at the modulator, means for transmittingadditional signals by the transmission of the carrier wave which issuppressed during the transmission of the intelligence, and means fortransmitting said additional signals through only a portion of one ofsaid lters.

2. In a carrier-wave system for transmitting intelligence from amodulator located at a transmitter station to a demodulator located at areceiver station by means of suppressed carrier modulated waves, atransmission line interconnecting said transmitter station and receiverstation, a band-pass lter connected between said modulator and saidtransmitting line, a band-pass lter connected between said demodulatorand said transmission line, both of said filters transmitting only oneof the two side bands generated at the modulator, means for transmittingadditional signals by the transmission of the carrier wave which issuppressed during the transmission of the intelligence, said meansincluding a source of the additional signals, and means for connectingsaid source directly to said transmission line.

3. In a carrier-wave system for transmitting intelligence from amodulator located at a transmitter station to a demodulator located at areceiver station by means of suppressed carrier modulated waves, atransmission line interconnecting said transmitter station and receiverstation, a band-pass filter connected between said modulator and saidtransmitting line, a band-pass filter connected between said demodulatorand said transmission line, both of said lters transmitting only one ofthe two side bands generated at the modulator, means for transmittingadditional signals by the transmission of the carrier wave which issuppressed during the transmission of the intelligence, one of saidfilters comprising a section connected to said transmission line andslightly attenuating the additional signals and a second section highlyattenuating the additional signals, and means for transmitting saidadditional signals through only the first section of said fllter.

4. In a carrier-wave system for transmitting intelligence from amodulator located at a transmitter station to a demodulator located at areceiver station by means of suppressed carrier modulated waves, atransmission line interconnecting said transmitter station and receiverstation, a band-pass filter connected between said modulator and saidtransmitting line, a band-pass lter connected between said demodulatorand said transmission line, both of said lters transmitting only one ofthe two side bands generated at the modulator, means for transmittingadditional signals by the transmission of the carrier wave which issuppressed during the transmission of the intelligence, one of saidfilters comprising a section connected to the transmitting line andslightly attenuating the additional signals and a second section highlyattenuating the additional signals, and means to pass said additionalsignals' through only the first section of said filter, including asignal circuit connected to a point between said sections, said ltersections exhibiting a high input impedance at said point.

THOMAS SAMUEL SKILIMAN.

